Technical Field
The present invention relates to rotation detector and a rotation detection method, and particularly to reduction of detection error due to eccentricity of a rotor.
Description of the Related Art
As a method of detecting an angle of a rotor such as a brushless motor, there is a method of using a magetoelectric transducer such as hall elements producing a signal having an amplitude in accordance with a magnetic field applied. Japanese published unexamined application No. JP-2013-002835-A discloses a method of determining an angle of a rotor generating a magnetic field with a magetoelectric transducer, based on an amplitude of a signal produced in accordance with a rotational angle of the rotor.
In order to reduce an angle error due to due to eccentricity of a rotor, Japanese published unexamined application No. JP-2013-002835-A also discloses a rotor including a magnet having a maximum length in a magnetization direction shorter than a maximum length in a direction perpendicular to a rotational axis of the rotor and the magnetization direction.
In detecting a rotational position of a rotor, it is important to consider an error of the rotor. When the method disclosed in Japanese published unexamined application No. JP-2013-002835-A is used, a design of the rotor is limited. Particularly, the brushless motor is required to increase the number of poles. However, the method disclosed in Japanese published unexamined application No. JP-2013-002835-A limits the number to two.